Circuit breaker with hydraulic operating mechanism for vacuum interrupter

ABSTRACT

A vacuum circuit breaker comprises three vacuum circuit interrupters, each having a pair of separable contacts therein, which are opened and closed by an operating mechanism. The operating mechanism comprises a separate operating rod connected to the movable contact of each interrupter and each operating rod has an opening acceleration spring connected thereto. All operating rods are driven to contact closed position by a main piston which is disposed in a hydraulic cylinder. Hydraulic fluid is supplied to the cylinder under great pressure by a high-speed gear pump, which is driven by a DC series-wound high speed electric motor, through a small orifice (containing a one-way check valve) located in a valve piston in the cylinder. The valve piston, which is spring-loaded, effects closure of a relatively large dump port leading from the cylinder. The valve piston is moved to open the dump port when the main piston is mechanically moved against the fluid in the cylinder by all operating rods as they are driven to contact open position by their accelerating springs. Closing of the circuit breaker is accomplished by energizing a closing solenoid which releases a first latch which allows a spring loaded motor control switch to close momentarily. Closure of the motor control switch starts the pump motor and the pump supplies hydraulic fluid to drive the main piston (and all operating rods) to contact closed position. Such movement allows a second latch to reset and engage a lever connected to the main piston to lock the latter (and the operating rods and contacts) in closed position. Resetting of the second latch also opens the motor control switch to stop the pump motor. Opening of the circuit breaker is accomplished by energizing a trip solenoid which releases a third latch which allows the second latch to be disengaged from the lever under the action of the opening acceleration springs on the operating rods as the latter move to open position. Such movement of the operating rods causes movement of the main piston, opening of the valve piston, and rapid dumping of the hydraulic fluid from the cylinder.

United States Patent Peck [ 1 July 4, 1972 [54] CIRCUIT BREAKER WITH HYDRAULIC OPERATING MECHANISM FOR VACUUM INTERRUPTER [72] Inventor: Henry L. Peek, Wellesley, Mass.

Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

22 Filed: Dec. 17,1970

211 Appl.No.: 98,972

[73] Assignee:

Primary Examiner-David Smith, Jr. Attorney-Thomas F. Kirby, Lee H. Kaiser and Robert B. Benson [5 7] ABSTRACT A vacuum circuit breaker comprises three vacuum circuit interrupters, each having a pair of separable contacts therein, which are opened and closed by an operating mechanism. The

operating mechanism comprises a separate operating rod connected to the movable contact of each interrupter and each operating rod has an opening acceleration spring connected thereto. All operating rods are driven to contact closed position by a main piston which is disposed in a hydraulic cylinder. Hydraulic fluid is supplied to the cylinder under great pressure by a highspeed gear pump, which is driven by a DC serieswound high speed electric motor, through a small orifice (containing a one-way check valve) located in a valve piston in the cylinder. The valve piston, which is spring-loaded, effects closure of a relatively large dump port leading from the cylinder. The valve piston is moved to open the dump port when the main piston is mechanically moved against the fluid in the cylinder by all operating rods as they are driven to contact open position by their accelerating springs.

Closing of the circuit breaker is accomplished by energizing a closing solenoid which releases a first latch which allows a spring loaded motor control switch to close momentarily. Closure of the motor control switch starts the pump motor and the pump supplies hydraulic fluid to drive the main piston (and all operating rods) to contact closed position. Such movement allows a second latch to reset and engage a lever connected to the main piston to lock the latter (and the operating rods and contacts) in closed position. Resetting of the second latch also opens the motor control switch to stop the pump motor.

Opening of the circuit breaker is accomplished by energizing a trip solenoid which releases a third latch which allows the second latch to be disengaged from the lever under the action of the opening acceleration springs on the operating rods as the latter move to open position. Such movement of the operating rods causes movement of the main piston, opening of the valve piston, and rapid dumping of the hydraulic fluid from the cylinder.

9 Claims, 4 Drawing Figures P'A'TE'N'TEDJUM 1972 3,674. 955

SHEET 10F 2 P'A'TENTEDJUH I972 sum or 2 CIRCUIT BREAKER WITH HYDRAULIC OPERATING MECHANISM FOR VACUUM INTERRUPTER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to circuit breakers having hydraulic operating mechanisms for operating vacuum type electric power circuit interrupters.

2. Description of the Prior Art Vacuum power circuit interrupters, which comprise a pair of separable contacts disposed in an evacuated envelope, incorporate certain features which require special attention in the design of the operating mechanisms used therewith. For example, some of these features are: very short contact stroke (about one-half inch); butt type rather than sliding type contacts; very short arcing time (about one-half cycle maximum). The short stroke and short arcing time permit the interrupter to be cleared in about one cycle total time (i.e., about one-half cycle of sensing and response time plus about one-half cycle of arcing time), provided there is almost instantaneous sensing of and response to a fault condition.

In a typical vacuum power circuit breaker, although the contact stroke of each interrupter is only approximately onehalf inch, the operating mechanism must provide approximately 50 percent additional stroke to compress the heavy contact compression springs which provide both the force necessary to prevent the contacts from being forced open magnetically during high momentary currents and the followup necessary to compensate for contact erosion, manufacturing variations, and temperature changes. Because of this, approximately two-thirds of the total closing stroke provided by the operating mechanism is performed against substantially zero reaction from the interrupter contacts. In fact, due to the vacuum maintained in the envelope in each interrupter, the interrupters actually exert a net closing force which must be opposed by an opening force provided by the operating mechanism. During the final one-third of the closing stroke (after the butt contacts touch) the operating mechanism must exert an extremely high force to compress the contact compression springs to overcome magnetic blow-off effects. The force required varies as the square of the momentary current that the breaker is rated to handle.

There are additional factors in the design of the operating mechanism which must also be taken into account. For example, delicate glass-to-metal or ceramic-to-metal seals require that the shock to which the vacuum interrupters are subjected be held to a minimum. Limitations of the bellows, which permit the contacts to move, require that overtravel be controlled. Since, contact rebound during closing both accelerates contact erosion and may cause the contacts to weld, it must be substantially eliminated. Opening rebound (with total gap length only on the order of one-half inch) must also be substantially eliminated. Achievement of one cycle total clearing time requires very light moving parts and, therefore,

- the most direct coupling possible between the interrupters and prime mover.

Prior art operating mechanisms have been of the purely mechanical type or the electromechanical type and, although generally satisfactory for their purpose, take into account one or more of the aforedescribed factors. It is desirable, therefore, to provide new and improved operating mechanisms for vacuum power circuit breakers which overcome the disadvantages of prior art operating mechanisms, take into account all of the aforesaid design criteria and have other advantages.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a vacuum circuit breaker which comprises at least one vacuum circuit interrupter, an operating mechanism therefor, and control means for effecting operation of the operating mechanism. The vacuum circuit interrupter comprises an evacuated envelope in which a pair of separable contacts, at

have been unable to least one of which is movable, are disposed. The operating mechanism comprises operating means for the interrupters, including contact opening acceleration means to effect contact separation, hydraulic means to efiect contact closure, and releasable latching means to maintain the breaker closed.

The operating means comprises contact pressure spring means connected between the movable contact and a rod, and an operating lever pivotably connected between the rod and the opening acceleration spring means.

The hydraulic system comprises a fluid reservoir or source for hydraulic fluid, a high-speed high-torque gear pump supplied from the reservoir, a cylinder and a piston movable in one direction to efiect closure of said contacts, a pump driven by an electric motor for supplying hydraulic fluid to said cylinder to move said piston in said one direction, and valve means for permitting fluid flow from said pump to said cylinder, said valve means allowing rapid dumping of fluid from said cylinder when said piston is moved in another direction by said contact opening acceleration means as said contacts are separated.

The latching means comprises a pivotally mounted spring biased closing latch movable from one position to another to actuate a spring-loaded motor control switch; a pivotably mounted spring biased holding latch having one position wherein it holds the lever (and thus the operating rod and contacts) in closed position; and a pivotably mounted spring biased trip latch having one position wherein it holds the holding latch in the latters one position.

The control mears comprises selectively operable closing coil contacts which control energization of a closing coil or solenoid which effects movement of the closing latch; a motor control switch movable to on position by movement of the closing latch to energize the pump motor and movable to off position by resetting of the holding latch; and selectively operable trip coil contacts which control energization of a trip coil or solenoid which effects operation of the trip latch.

During closing, the closing solenoid is energized by the closing contacts which releases the first latch thereby allowing the spring loaded motor control switch to close momentarily. Closure of the motor control switch starts the pump motor and the pump rapidly supplies hydraulic fluid to drive the main piston (and all operating rods) quickly to contact closed position. Such movement allows the holding latch to reset and engage a lever connected to the operating rods to lock the latter (and the contacts) in closed position. Resetting of the holding latch also reopens the motor control switch to stop the pump motor.

During opening, the trip solenoid is energized by the trip coil contacts which releases the trip latch thereby allowing the holding latch to be disengaged from the lever by the action of the opening acceleration spring means. This effects movement of the operating rods and causes movement of the main piston, opening of the valve piston, and rapid dumping of the hydraulic fluid from the cylinder.

OBJECTS It is an object of the present invention to provide new and improved electric circuit breakers and, particularly, vacuum type electric power circuit breakers employing vacuum interrupters which use hydraulic operating mechanisms.

Another object is to provide operating mechanisms of the aforesaid character which have very short sensing and response times during both opening and closing operations of the circuit breaker.

Another object is to provide operating mechanisms of the aforesaid character which provide minimum shock to the circuit interrupters during both opening and closing.

Another object is to provide controlled overtravel for those portions of the operating mechanisms which effect contact movement and substantially eliminate contact rebound.

Another object is to provide operating mechanisms of the aforesaid character which have relatively light moving parts and employ direct coupling between the prime mover in the operating mechanism and the circuit breaker contacts.

Another object is to provide operating mechanisms of the aforesaid character which exert extremely high and rapid forces during contact closing and opening.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawings illustrate a preferred embodiment of the invention but it is to be understood that the embodiment illustrated is susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is an end elevational view of a portion of a circuit breaker in accordance with the present invention;

FIG. 2 is a side elevational view taken along line II-II of FIG. 1;

FIG. 3 is an enlarged cross-sectional view of a cylinder and valve of the circuit breaker operating mechanism taken along line III-III of FIG. 2;

FIG. 4 is a schematic diagram of a portion of a closing control means and tripping control means for the circuit breaker shown in FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 of the drawing, the numeral designates a vacuum circuit breaker in accordance with the invention which is understood to be used in a relatively high voltage multiphase circuit to interrupt the circuit either automatically upon the occurrence of certain fault conditions or upon command and to reclose the circuit upon command.

As FIG. 1 shows circuit breaker 10 comprises a suitable framework or support 12 upon which a plurality (three) vacuum interrupters l4, l6 and 18 are rigidly mounted; an operating mechanism 20 for opening and closing the interrupters; and a control means 22 (shown separately in FIG. 4) for actuating the operating mechanism.

Since the vacuum interrupters 14, 16 and 18 are identical, a description of interrupter 16 will suffice for the other two. As FIG. 2 shows, interrupter 16 comprises a sealed evacuated insulating envelope 24 in which a stationary contact 26 and a movable contact 28 are disposed and these contacts are electrically connected to line and load terminals 30 and 32,

respectively.

Operating mechanism 20 comprises a plurality of operating means 34, 36 and 38 for the interrupters l4, l6 and 18, respectively, shown in FIG. 1; a hydraulic means or system 40, shown in FIGS. 1, 2 and 3 considered together, for cooperation with the operating means to effect circuit breaker closing; and releasable latching means 42, as shown in FIG. 2, for maintaining circuit breaker 10 in closed condition.

Since the operating means 34, 36 and 38 are identical, a description of operating means 36 will sufiice for the other two. As FIGS. 1 and 2 show, operating means 36 comprises an insulated operating rod 44 which is connected at its upper end to a contact pressure assembly or means 46 and at its lower end to a link 48. Contact pressure assembly 46 comprises a first link 50 which has one end pivotally mounted on a pin 52 on circuit breaker support 12 and which has its other end pivotally connected to a pin 54 on movable contact 28 of vacuum interrupter 16. A second link 56 is provided which has one end pivotally mounted on pin 54. Link 56 carries a contact pressure or compression spring 60 which is disposed between an abutment or projection 62 on link 56 and a slidable member 64 on link 56. A third link 66 is provided, in the form of a triangular plate, which has one corner pivotally mounted on pin 52; a second comer pivotally mounted on a pin 68 on slidable member 64; and a third comer pivotally mounted on a pin 69 on the upper end of operating rod 44. During upward (closing) movement of operating rod 44, third link 66 forces slidable member 64 along link 56 against the force of spring 60 and the latter acts upon abutment 62 to close the movable contact 28 of circuit interrupter 16. Spring 60 allows for overtravel of operating rod 44 and, when charged, exerts a predetermined amount of pressure against contact 28. Link 48, hereinbefore referred to and to which operating rod 44 is pivotally connected, is pivotally connected to one end of a lever 70 by a pin 71. Lever 70 is rigidly mounted on a shaft 72 which is rotatably mounted on support 12. The other end of lever 70 is pivotally connected to a contact opening acceleration assembly 74. Assembly 74 comprises a movable link 76 which is pivotally connected by a pin 78 to the said other end of lever 70. Link 76 is provided with an abutment or projection 80 and an opening acceleration or compression spring 82 is disposed between this abutment 80 and framework 12 of circuit breaker 10. When lever 70 is unlatched, as hereinafter explained, spring 82 causes clockwise rotation of lever 70 and rotation of shaft 72 and downward movement of all operating rods and opening of the contacts of the vacuum interrupters 14, 16 and 18. It is to be understood that only lever 70 is latchable directly by latching means 42.

The hydraulic system 40 which efiects closing (upward) movement of the operating rods, such as rod 44, and closure of the contacts in the vacuum interrupters 14, 16 and 18 comprises a reservoir 86 containing a supply of hydraulic fluid; a pump 88, preferably a gear type high speed, high torque pump, connected to the reservoir by a supply line 90; a hydraulic ram unit 92 having a valve unit 94 connected thereto; an inlet line 96 connected between pump 88 and valve unit 94; and a return line 98 connected between valve unit 94 and reservoir 86. Hydraulic ram unit 92 comprises a cylinder 100 having a piston 102 therein and the latter, which is provided with a projection 104 on one side, is also provided with a rod portion 106 which is mechanically connected to link 48 of operating mechanism 20. As FIG. 3 shows, valve unit 94 comprises a valve body 110 having a cylindrical chamber 112 therein in which a valve piston 114 is disposed. Chamber 112 communicates with inlet line 96. Valve piston 114 is provided with a passageway 116 therethrough which is controlled by a one-way or check valve in the form of a ball 1 17 located in the passageway. Valve body 1 10 is further provided with an annular chamber 1 18 which surrounds cylindrical chamber 112. Annular chamber 118 communicates with return line 98 and also can communicate with cylinder 100 of ram unit 92 through a dump port 120 which is normally closed by valve piston 114 which is biased by a compression spring 122 in chamber 112. During a circuit breaker closing operation hydraulic fluid flows from reservoir 86 to pump 88 which supplies it at high pressure through inlet line 96 to valve unit 94 which permits it to flow through passageway 116 in valve piston 114 into cylinder 100 of ram unit 92 thereby causing upward movement of piston 102. During a circuit breaker opening operation, piston 102 is forced downward, as hereinafter explained, and the fluid in cylinder 100 forces ball 117 to close passageway 116 and also forces valve piston 114 to open dump port 120. Thus, fluid is rapidly discharged from cylinder 100 to reservoir 86.

The latching means 42 of circuit breaker 10 comprise three latch members 124, 126 and 128, each of which is pivotally mounted on or with respect to framework 12 of the circuit breaker, as FIG. 2 shows.

As FIGS. 2 and 4 show, the control means 22 of circuit breaker l0 cooperate with latching means 42 and comprise an electric motor 130 (preferably a series-wound high speed high torque motor) for driving pump 88; a motor control switch 132 for energizing and deenergizing the motor; a closing coil or solenoid 134 for moving closing latch 124 from one position wherein it maintains motor control switch 132 open to another position wherein it allows switch 132 to close; a tripping coil or solenoid 136 for moving trip latch 128 from one position wherein it maintains holding latch 126 in set position to another position wherein it releases holding latch 126; a closing contact 138 for energizing closing coil 134 from the terminals 140 and 142 of an electrical power source; and a tripping contact 143 for energizing tripping coil 136 from the terminals 140 and 142 of the power source.

Closing latch 124 is L-shaped and pivots about a point 144. In its closed position (show in FIG. 2) into which it is biased by a tension spring 146, closing latch 124 maintains motor control switch 132 open. Holding latch 126 is also L-shaped and pivots about a point 148. Holding latch 126 is returned to its closed position (shown in FIG. 2) under a roller 150 on lever 70 by the bias of a compression spring 152. It is maintained in its closed position against the bias of breaker accelerating springs by tripping latch 128, which, in its closed position bears against a roller 154 on holding latch 12. Tripping latch 128 is biased to its closed position (shown in FIG. 2) by a tension spring 156. Holding latch 126 is provided in its horizontal arm with a slot 127.

Circuit breaker operates as follows.

OPENING OPERATION Assume first that circuit breaker 10 is initially closed, as shown in FIG. 1. When trip magnet 136 is energized, through control switch contact 143 in response to a fault or overload, the trip plunger drives trip latch 128 clockwise releasing holding latch 126 which in turn releases roll 150 permitting breaker 10 to open. The contact pressure springs 60 provide most of the initial opening impulse force and the opening accelerating spring 82 provides the follow-through force to complete the opening stroke and to hold the circuit interrupter contacts open against atmospheric pressure.

In order to achieve one cycle interruption time, it is necessary that the hydraulic fluid behind main piston 102 in cylinder 100 be unobstructed in its flow back to reservoir 86. If the fluid should be required to return back along the same path through which it flowed during the closing stroke; i.e., through passageway 1 16, tubing 96 between valve unit 94 and gearpump 88, and backward through the gearpump itself, it would be impossible to obtain sufficient breaker opening speed. However, sliding valve piston 114 is forced downward by fluid pressure in cylinder 100 to open dump port 120 and makes possible a rapid release of pressure so that the fluid offers substantially zero retarding force to the breakers opening operation. More specifically, the opening force from contact pressure spring 60 and opening acceleration spring 82 drives piston 102 downward. The pressure caused by this movement in the fluid below piston 102 forces ball 117 into a position to block passageway 116 and causes valve piston 114 to move downward thereby opening dump port 120. Dump port 120 and chamber 118 are large in cross-section and the latter completely surrounds piston 114 and connects, through line 98 directly back to reservoir 86. It will be observed from FIG. 3 that the escape area through the above described path is so large that substantially no retarding force is offered by fluid pressure and, therefore, breaker 10 opens unobstructedly. However, as full open position of piston 102 is approached, tapered projection 104 on piston 102 enters dump port 120 in valve body 110 and during the last increment of opening stroke acts as a dashpot by diminishing the usable cross-section of dump port 120, passing the trapped fluid in the annular area around projection 104 more slowly through to reservoir 86, thus absorbing the remaining opening kinetic energy, eliminating shock, and preventing rebound.

CLOSING OPERATION horizontal portion of holding latch 126 and closing latch 124 can hold motor control switch 132 open even through holding latch 126 has already been released to open the breaker.

To close circuit breaker 10, closing contact 138 is closed either manually or automatically to energize closing coil 134.

Closing coil 134 then moves closing latch 124 counterclockwise thereby permitting motor control switch contact 132 to snap closed and this energizes motor 130 which is a series motor capable of very high speed at light loads and of very heavy torque at heavy loads. Motor 130 drives gearpump 88 which draws hydraulic fluid from reservoir 86 and forces the fluid at high pressure through line 96 to valve unit 94. The pressure in cylinder 112 under valve piston 114 holds the valve piston tightly against its seat preventing any escape of oil through dump port back to reservoir 86. Simultaneously, the pressure under ball 117 lifts it off its seat in valve piston 114 permitting the high pressure fluid to flow through passageway 116 to raise main piston 102 thus close circuit breaker 10.

As circuit breaker 10 reaches closed position, holding latch 126 is forced in place under roll 150 by its reset spring 152 and trip latch 128 is forced behind roll 154 by its reset spring 156. The reset spring 152 of holding latch 126 has sufficient force to reset motor control switch 132 to its open position thus deenergizing motor 130. When motor is deenergized, the total force load imposed by the contact pressure springs 60 causes roll to exert a clockwise torque on holding latch 126. The cooperating face of latch 126 is understood to be ground about a center which is to the right of the center 148 about which holding latch 126 rotates. Trip latch 128 prevents holding latch 126 from rotating clockwise under this torque. This second stage of latch force reduction is provided to permit a small, fast trip coil 136 to be used. As soon as main piston 102 reaches the top of cylinder 100 during the closing stroke, motor 130 is deenergized and there is practically no coasting of gearpump 88 and motor 130 because the fluid no longer has any place to go and they stop almost instantly. If circuit breaker 10 were closing against a short circuit, trip coil 136 would be energized immediately by the control means 22 and the instantaneous stopping of motor 130 and pump 88 insure that the prime mover causes no delay in immediate opening of circuit breaker 10.

I claim 1. In combination with a vacuum circuit breaker having a pair of contacts one of which is stationary and the other is movable relative to said stationary contact;

hydraulic operating means for said pair of contacts including a hydraulic motor housing having a cylinder therein and inlet and exhaust ports communicating with said cylinder and a piston reciprocable within said cylinder;

a dump valve within said housing operable by fluid from said inlet port to a first position wherein it closes said exhaust port, said dump valve carrying a check valve permitting flow of fluid from said inlet port into said cylinder;

a pump connected to said inlet port;

a series electric motor for operating said pump;

contact pressure means coupled to said movable contact for alternately closing said contacts under high pressure engagement and for disengaging said contacts and including a compression spring and a spring loading member movable in a first direction to load said compression spring and close said contacts and also movable in the opposite direction to open said contacts; and,

force transmitting means including a reciprocable operating rod positively connecting said piston and said movable spring loading member,

said check valve being adapted to be closed by the fluid pressure exerted within said cylinder by said piston when said contact pressure means open said contacts and said dump valve being actuated by said fluid pressure to a second position wherein it blocks said inlet port and opens said exhaust port.

2. In the combination according to claim 1 wherein there is provided a releasable holding latch operable to engage said force transmitting means to maintain said contacts in closed position;

a closing latch;

an electric switch operably connected to regulate the operation of said electric motor, said switch being maintained open by said closing latch to thereby maintain said electric motor de-energized;

spring means for urging said switch to closed position;

means operable to effect the release of said holding latch to permit said contact pressure means to open said contacts; and,

means operable to actuate said closing latch to release said switch for energizing said electric motor to drive said pump to supply fluid under pressure to said cylinder for operating said piston in a contact closing operatiq 3. In the combination according to claim 2 wherein there is provided reset means for moving said holding latch to its initial position in engagement with said force transmitting means, said holding latch being operable when moved to its reset initial position to open said switch, thereby interrupting the delivery of fluid under pressure to said cylinder; and,

means operable to reset said closing latch for maintaining said switch open.

4. In the combination according to claim 1 wherein there is provided an acceleration spring;

a second force transmitting means coupling said acceleration spring to said first force transmitting means in a manner that upon operation of said compression spring to open said contacts said acceleration spring cooperates in said contact opening operation and to move said piston in a second direction, said second force transmitting means being operable to load said acceleration spring when said spring loading member is moved in a direction to load said compression spring.

5. In the combination according to claim 4 wherein said second force transmitting means is a lever having one arm operatively coupled to said accelerating spring and having its opposite arm operatively coupled to said first force transmitting means.

6. In the combination according to claim 3 wherein said switch is provided with an actuating member and said holding latch is an L-shaped member having one arm thereof in engagement with said force transmitting means and its second arm in engagement with the actuating member of said switch;

spring means operably engaged with the second arm of said holding latch and operable to bias said holding latch into engagement with said force transmitting means and the actuating member of said switch;

said closing latch is an L-shaped member having one arm thereof in engagement with the actuating member of said switch for maintaining said switch open when said holding latch is moved out of engagement with said force transmitting means;

and said means for actuating said closing latch operates on the second arm of said closing latch to move said first arm to release the actuating member'of said switch to actuate said switch; and

spring means operable to apply a biasing force to said second arm of said closing latch for resetting said closing latch.

7. In a combination according to claim 1 wherein there is provided dashpot means carried by said piston and cooperable with said dump valve upon the last increment of the contact opening operation to diminish the cross section of said exhaust port thereby reducing the rate of flow of the exhaust fluid to slow piston travel to prevent contact rebound and eliminate shock.

8. In combination with a vacuum circuit breaker having a pair of contacts one of which is stationary and the other is movable relative to said stationary contact;

contact pressure applying means for alternately actuating said movable contact into high pressure engagement with said stationary contact and for disengaging it from said stationary contact and including a compression spring and a spring loading member movable in a first direction to load said compression spring to thus close said contacts and also movable in the opposite direction to unload said s rin and open said contacts; by a re operating means for said pair of contacts including a hydraulic ram housing having a cylinder therein and inlet and exhaust ports and a piston reciprocable within said cylinder;

a source of fluid under pressure connected to said inlet port;

force transmitting means including a reciprocable operating rod positively connecting said piston and said movable spring loading member;

a pivoted lever operatively connected adjacent one end to said operating rod;

contact opening accelerating spring means engaging the opposite end of said lever for urging said lever in a direction to open said contacts;

releasable latching means engaging said lever for holding said contacts in closed position; and,

dump valve means within said housing operable by fluid pressure exerted by said piston when said contacts are being opened to block said inlet port and to open said exhaust port and also operable by fluid under pressure from said inlet port to block said exhaust port and permit flow of said fluid under pressure into said cylinder to actuate said piston in a direction to close said contacts.

9. In the combination of claim 8 wherein said source of fluid under pressure includes a gear pump connected to said inlet port, a series electric motor for driving said pump, and electric switch means controlled by said lever for controlling the deenergization of said electric motor. 

1. In combination with a vacuum circuit breaker having a pair of contacts one of which is stationary and the other is movable relative to said stationary contact; hydraulic operating means for said pair of contacts including a hydraulic motor housing having a cylinder therein and inlet and exhaust ports communicating with said cylinder and a piston reciprocable within said cylinder; a dump valve within said housing operable by fluid from said inlet port to a first position wherein it closes said exhaust port, said dump valve carrying a check valve permitting flow of fluid from said inlet port into said cylinder; a pump connected to said inlet port; a series electric motor for operating said pump; contact pressure means coupled to said movable contact for alternately closing said contacts under high pressure engagement and for disengaging said contacts and including a compression spring and a spring loading member movable in a first direction to load said compression spring and close said contacts and also movable in the opposite direction to open said contacts; and, force transmitting means including a reciprocable operating rod positively connecting said piston and said movable spring loading member, said check valve being adapted to be closed by the fluid pressure exerted within said cylinder by said piston when said contact pressure means open said contacts and said dump valve being actuated by said fluid pressure to a second position wherein it blocks said inlet port and opens said exhaust port.
 2. In the combination according to claim 1 wherein there is provided a releasable holding latch operable to engage said force transmitting means to maintain said contacts in closed position; a closing latch; an electric switch operably connected to regulate the operation of said electric motor, said switch being maintained open by said closing latch to thereby maintain said electric motor de-energized; spring means for urging said switch to closed position; means operable to effect the release of said holding latch to permit said contact pressure means to open said contacts; and, means operable to actuate said closing latch to release said switch for energizing said electric motor to drive said pump to supply fluid under pressure to said cylinder for operating said piston in a contact closing operation.
 3. In the combination according to claim 2 wherein there is provided reset means for moving said holding latch to its initial position in engagement with said force transmitting means, said holding latch being operable when moved to its reset initial position to open said switch, thereby interrupting the delivery of fluid under pressure to said cylinder; and, means operaBle to reset said closing latch for maintaining said switch open.
 4. In the combination according to claim 1 wherein there is provided an acceleration spring; a second force transmitting means coupling said acceleration spring to said first force transmitting means in a manner that upon operation of said compression spring to open said contacts said acceleration spring cooperates in said contact opening operation and to move said piston in a second direction, said second force transmitting means being operable to load said acceleration spring when said spring loading member is moved in a direction to load said compression spring.
 5. In the combination according to claim 4 wherein said second force transmitting means is a lever having one arm operatively coupled to said accelerating spring and having its opposite arm operatively coupled to said first force transmitting means.
 6. In the combination according to claim 3 wherein said switch is provided with an actuating member and said holding latch is an L-shaped member having one arm thereof in engagement with said force transmitting means and its second arm in engagement with the actuating member of said switch; spring means operably engaged with the second arm of said holding latch and operable to bias said holding latch into engagement with said force transmitting means and the actuating member of said switch; said closing latch is an L-shaped member having one arm thereof in engagement with the actuating member of said switch for maintaining said switch open when said holding latch is moved out of engagement with said force transmitting means; and said means for actuating said closing latch operates on the second arm of said closing latch to move said first arm to release the actuating member of said switch to actuate said switch; and spring means operable to apply a biasing force to said second arm of said closing latch for resetting said closing latch.
 7. In a combination according to claim 1 wherein there is provided dashpot means carried by said piston and cooperable with said dump valve upon the last increment of the contact opening operation to diminish the cross section of said exhaust port thereby reducing the rate of flow of the exhaust fluid to slow piston travel to prevent contact rebound and eliminate shock.
 8. In combination with a vacuum circuit breaker having a pair of contacts one of which is stationary and the other is movable relative to said stationary contact; contact pressure applying means for alternately actuating said movable contact into high pressure engagement with said stationary contact and for disengaging it from said stationary contact and including a compression spring and a spring loading member movable in a first direction to load said compression spring to thus close said contacts and also movable in the opposite direction to unload said spring and open said contacts; hydraulic operating means for said pair of contacts including a hydraulic ram housing having a cylinder therein and inlet and exhaust ports and a piston reciprocable within said cylinder; a source of fluid under pressure connected to said inlet port; force transmitting means including a reciprocable operating rod positively connecting said piston and said movable spring loading member; a pivoted lever operatively connected adjacent one end to said operating rod; contact opening accelerating spring means engaging the opposite end of said lever for urging said lever in a direction to open said contacts; releasable latching means engaging said lever for holding said contacts in closed position; and, dump valve means within said housing operable by fluid pressure exerted by said piston when said contacts are being opened to block said inlet port and to open said exhaust port and also operable by fluid under pressure from said inlet port to block said exhaust port and permit flow of said fluid under pressure into said cylinder to actuate said piston in a direction to close said contacts.
 9. In the combination of claim 8 wherein said source of fluid under pressure includes a gear pump connected to said inlet port, a series electric motor for driving said pump, and electric switch means controlled by said lever for controlling the de-energization of said electric motor. 